The present invention relates to a method for testing for leaks in freeze-drying systems and to freeze-drying apparatus for performing the method.
Freeze-drying apparatus usually includes a chamber equipped with product shelves for containers holding the product to be lyophilized. These product shelves are heatable because heat must be provided for the product to be lyophilized to accelerate the drying process. Frequently, such product shelves are also coolable allowing the freezing required in the freeze-drying process to take place within the chamber. Cooling and/or heating of the product shelves can be performed with the aid of liquids (brines, bases, silicone oil, or the like) or vapors. For this purpose, the product shelves are provided with flow channels or double walls. The product shelves are supplied with the heat-exchange medium by way of conduits connected to the product shelves brought through the walls of the freeze-drying chamber.
The freeze-drying process is performed under a vacuum. Therefore, devices for producing a vacuum and for dissipating the vapors developed during the drying are connected to the freeze-drying chamber. Generally, a second chamber accommodating a condenser is connected to the freeze-drying chamber and is coupled to a vacuum pump.
Freeze-drying processes are preferentially employed in the manufacture of medicinal preparations. The value of a charge is frequently very high: it is often in excess of one million dollars. The protection of such a charge against contamination which could occur, for example, due to leaks in the conduit system for the heating and/or cooling medium is therefore of particular significance.
German Offenlegungsschrift (nonexamined published application) 3,230,146 discloses the testing of closed pipeline systems for leaks in that the tightly closed system is pressurized with a fluid, pressure is maintained over a longer period of time and this pressure is monitored by means of a measuring instrument. The tested system is tight if no drop in pressure occurs.
Leak detection of this type is relatively insensitive. Moreover, the systems to be monitored in this manner must be designed so that they are able to withstand a relatively high testing pressure. Finally, it is generally impossible to continuously monitor the pipeline system for leaks while it is in operation because it would require constant maintenance of the test pressure.